The present invention relates generally to methods of forming metal structures in semiconductor devices and specifically to methods of using a dry cleaning method instead of a traditional wet clean method after metal etch.
Prevention of metal corrosion and pitting defects with conventional wet cleaning methods after metal etching is difficult. Wet cleaning methods can leave chlorine (Cl2) trapped in a thin sidewall polymer which maximizes corrosion and pitting of, for example, an aluminum (Al) or aluminum alloy substrate. If a thicker sidewall polymer is formed to minimize the exposure of the aluminum/aluminum alloy substrate to Cl2, the difficulty of a more narrow window within which to perform the wet clean arises.
Therefore, passivation (formation of the sidewall polymer within the etched structure) during dry etching and clean step is a critical step. Sometimes an adequate passivation step followed by a poor clean step will also cause pitting and corrosion. With device dimensions, or design rule, getting smaller and smaller, the influence of any such defects on device performance and reliability is becoming greater and greater.
In high ion density reactors using high power processes, certain problems present. One such problem is a high rate of resist erosion and loss of a substantial amount of substrate dielectric, generally silicon oxide (SiO2). This process also is more prone to corrosion known as xe2x80x9cmouse bitesxe2x80x9d characterized as an undesirable lateral loss of Al(Cu).
Another problem is that a metal to tungsten (W) galvanic reaction erodes the interface of the metal Al(Cu) and the W stud. This leads to the loss of W and an increased Rc.
A further problem is the ring type residue, or when a high Rc occurs at the wafer edge due to penetration of TiN from an ACT wet clean.
Also, metal corrosion can occur that is caused by the reaction of chlorine gas and humidity to form HCl acid.
U.S. Pat. No. 4,501,061 to Wonnacott et al. describes a method for stripping an organic photoresist layer from a semiconductor device using CF4 and O2 plasma. The photoresist layer is oxidized with oxygen plasma and residual sulfur species are subsequently removed using a fluorine-containing plasma.
U.S. Pat. No. 5,378,653 to Yanagida describes a method of forming an Al-based pattern whereby dry etching with high selectively of an Al-based metallization layer and effective preventive measures for after-corrosion can be realized. If after etching residual chlorine is removed by O2 plasma ashing or plasma processing using a fluorine based gas, durability to after-corrosion can be improved further.
U.S. Pat. No. 5,599,743 to Nakagawa et al. describes a method of manufacturing a semiconductor device that includes etching an aluminum or alloy film through a mask by chlorination and/or bromination with plasma. The film is exposed to either: a gas plasma not liable to deposit or oxidize, but capable of substituting fluoride for chloride and/or bromide; or a gas mixture plasma comprising hydrogen and the above mentioned gas. The device is then washed with water and the mask is removed.
U.S. Pat. No. 5,976,986 to Naeem et al. describes a low pressure and low power Cl2/HCl process for sub-micron metal etching. Cl2 and HCl are used as reactant species by creating a transformer coupled plasma with power applied to electrodes positioned both above and below a substrate with metallization thereon to be etched. Three layer metallizations which include bulk aluminum or aluminum alloy sandwiched between barrier layers made from, for example, Ti/TiN, are etched in a three step process wherein relatively lower quantities of Cl2 are used in the plasma during etching of the barrier layers and relatively higher quantities of Cl2 are used during etching of the bulk aluminum or aluminum alloy layer. The ratio of etchants Cl2 and HCl and an inert gas, such as N2, are controlled in a manner such that a very thin sidewall layer (10-100 xc3x85) of reaction byproducts during RIE are deposited on the sidewalls of trenches within the etched metallization. The process does not use magnetic fields during etching.
U.S. Pat. No. 5,908,319 to Xu et al. describes forming a microwave plasma in a microwave downstream process from a gas that has a small quantity of fluorine to enhance ashing without substantial oxide loss. This process may be performed before or after other microwave downstream processes or reactive ion etching processes.
U.S. Pat. No. 5,795,831 to Nakayama et al. describes a method of removing a resist layer including a reactive ion etch (RIE) process and a downstream microwave process each performed at a wafer temperature no greater than about 60xc2x0 C. The low temperature precludes having to pre-heat the resist to drive off solvents.
U.S. Pat. No. 5,709,757 to Hatano et al. describes a dry clean.
U.S. Pat. No. 6,017,826 to Zhou et al. describes a method for forming a patterned layer within a microelectronics fabrication. A first plasma etch method is used to etch a blanket hard mask using an overlying patterned photoresist layer as a first etch mask layer, while exposing a blanket chlorine containing plasma etchable layer. A second plasma etch method is used to etch the exposed blanket chlorine containing plasma etchable layer using at least the patterned blanket hard mask layer as a second etch mask layer. The second plasma etch sidewall passivation layer is formed upon a sidewall of the patterned chlorine containing plasma etchable layer. A third plasma etch method strips the sidewall passivation layer while sequentially oxidizing the sidewall of the patterned chlorine containing plasma etchable layer. The third plasma etch method employs a third etchant gas composition which, upon plasma activation, forms an oxygen containing oxidizing species.
U.S. Pat. No. 5,882,489 to Bersin et al. describes a method for removing a resist while avoiding the use of acids and industrial solvents. Plasma is used to remove organic compounds. The device is rinsed in deionized water (DI), and it is then sputtered with argon to remove inorganic compounds. The order of DI rinsing and argon sputtering may be reversed.
U.S. Pat. No. 5,578,133 to Sugino et al. describes a dry cleaning process for removing metal contaminants from a surface of an oxide film. A reaction area is formed on the oxide film such that a silicon surface is formed corresponding to the reaction area. A dry cleaning gas is supplied to the oxide film including the reaction area to produce silicon halide molecules. The dry cleaning gas being selected from the group essentially consisting of chlorine, bromine, hydrogen chloride, hydrogen bromide, and a mixture thereof. The silicon halide molecules so formed are supplied to a surface of the oxide film and metal elements existing on the surface of the oxide film are removed.
Accordingly, it is an object of the present invention to provide an improved dry cleaning method after metal etch to prevent metal corrosion and pitting.
Another object of the present invention is to provide an improved dry cleaning method after metal etch to lower the defect density and engineering repair time.
It is a further object of the present invention to provide a fluorine containing gas/oxygen containing gas dry cleaning method without a downstream microwave power that uses magnetic power, a relatively low pressure, and medium bias RF power.
Other objects will appear hereinafter.
It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, an etched metallization structure is provided and placed in a processing chamber. The etched metallization structure is cleaned by introducing a fluorine containing gas/oxygen containing gas mixture into the processing chamber proximate the etched metallization structure without the use of a downstream microwave while applying a magnetic field proximate the etched metallization structure and maintaining a pressure of less than about 50 millitorr within the processing chamber for a predetermined time.